cub/util_vsmem.cuh

File members: cub/util_vsmem.cuh

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#pragma once

#include <cub/config.cuh>

#if defined(_CCCL_IMPLICIT_SYSTEM_HEADER_GCC)
#  pragma GCC system_header
#elif defined(_CCCL_IMPLICIT_SYSTEM_HEADER_CLANG)
#  pragma clang system_header
#elif defined(_CCCL_IMPLICIT_SYSTEM_HEADER_MSVC)
#  pragma system_header
#endif // no system header

#include <cub/util_arch.cuh>
#include <cub/util_device.cuh>
#include <cub/util_ptx.cuh>
#include <cub/util_type.cuh>

#include <cuda/discard_memory>
#include <cuda/std/type_traits>

#include <cstdint>

CUB_NAMESPACE_BEGIN

#ifndef _CCCL_DOXYGEN_INVOKED // Do not document

namespace detail
{

struct vsmem_t
{
  void* gmem_ptr;
};

template <typename AgentT>
class vsmem_helper_impl
{
private:
  // Per-block virtual shared memory may be padded to make sure vsmem is an integer multiple of `line_size`
  static constexpr std::size_t line_size = 128;

  // The amount of shared memory or virtual shared memory required by the algorithm's agent
  static constexpr std::size_t required_smem = sizeof(typename AgentT::TempStorage);

  // Whether we need to allocate global memory-backed virtual shared memory
  static constexpr bool needs_vsmem = required_smem > max_smem_per_block;

  // Padding bytes to an integer multiple of `line_size`. Only applies to virtual shared memory
  static constexpr std::size_t padding_bytes =
    (required_smem % line_size == 0) ? 0 : (line_size - (required_smem % line_size));

public:
  // Type alias to be used for static temporary storage declaration within the algorithm's kernel
  using static_temp_storage_t = ::cuda::std::_If<needs_vsmem, cub::NullType, typename AgentT::TempStorage>;

  // The amount of global memory-backed virtual shared memory needed, padded to an integer multiple of 128 bytes
  static constexpr std::size_t vsmem_per_block = needs_vsmem ? (required_smem + padding_bytes) : 0;

  static _CCCL_DEVICE _CCCL_FORCEINLINE typename AgentT::TempStorage&
  get_temp_storage(typename AgentT::TempStorage& static_temp_storage, vsmem_t&)
  {
    return static_temp_storage;
  }

  static _CCCL_DEVICE _CCCL_FORCEINLINE typename AgentT::TempStorage&
  get_temp_storage(typename AgentT::TempStorage& static_temp_storage, vsmem_t&, std::size_t)
  {
    return static_temp_storage;
  }

  static _CCCL_DEVICE _CCCL_FORCEINLINE typename AgentT::TempStorage&
  get_temp_storage(cub::NullType& static_temp_storage, vsmem_t& vsmem)
  {
    return *reinterpret_cast<typename AgentT::TempStorage*>(
      static_cast<char*>(vsmem.gmem_ptr) + (vsmem_per_block * blockIdx.x));
  }

  static _CCCL_DEVICE _CCCL_FORCEINLINE typename AgentT::TempStorage&
  get_temp_storage(cub::NullType& static_temp_storage, vsmem_t& vsmem, std::size_t linear_block_id)
  {
    return *reinterpret_cast<typename AgentT::TempStorage*>(
      static_cast<char*>(vsmem.gmem_ptr) + (vsmem_per_block * linear_block_id));
  }

  template <bool needs_vsmem_ = needs_vsmem, typename ::cuda::std::enable_if<!needs_vsmem_, int>::type = 0>
  static _CCCL_DEVICE _CCCL_FORCEINLINE bool discard_temp_storage(typename AgentT::TempStorage& temp_storage)
  {
    return false;
  }

  template <bool needs_vsmem_ = needs_vsmem, typename ::cuda::std::enable_if<needs_vsmem_, int>::type = 0>
  static _CCCL_DEVICE _CCCL_FORCEINLINE bool discard_temp_storage(typename AgentT::TempStorage& temp_storage)
  {
    // Ensure all threads finished using temporary storage
    CTA_SYNC();

    const std::size_t linear_tid   = threadIdx.x;
    const std::size_t block_stride = line_size * blockDim.x;

    char* ptr    = reinterpret_cast<char*>(&temp_storage);
    auto ptr_end = ptr + vsmem_per_block;

    // 128 byte-aligned virtual shared memory discard
    for (auto thread_ptr = ptr + (linear_tid * line_size); thread_ptr < ptr_end; thread_ptr += block_stride)
    {
      cuda::discard_memory(thread_ptr, line_size);
    }
    return true;
  }
};

template <class DefaultAgentT, class FallbackAgentT>
constexpr bool use_fallback_agent()
{
  return (sizeof(typename DefaultAgentT::TempStorage) > max_smem_per_block)
      && (sizeof(typename FallbackAgentT::TempStorage) <= max_smem_per_block);
}

template <typename DefaultAgentPolicyT,
          typename DefaultAgentT,
          typename FallbackAgentPolicyT = DefaultAgentPolicyT,
          typename FallbackAgentT       = DefaultAgentT,
          bool UseFallbackPolicy        = use_fallback_agent<DefaultAgentT, FallbackAgentT>()>
struct vsmem_helper_with_fallback_impl : public vsmem_helper_impl<DefaultAgentT>
{
  using agent_t        = DefaultAgentT;
  using agent_policy_t = DefaultAgentPolicyT;
};
template <typename DefaultAgentPolicyT, typename DefaultAgentT, typename FallbackAgentPolicyT, typename FallbackAgentT>
struct vsmem_helper_with_fallback_impl<DefaultAgentPolicyT, DefaultAgentT, FallbackAgentPolicyT, FallbackAgentT, true>
    : public vsmem_helper_impl<FallbackAgentT>
{
  using agent_t        = FallbackAgentT;
  using agent_policy_t = FallbackAgentPolicyT;
};

template <typename DefaultPolicyT, typename FallbackPolicyT, template <typename...> class AgentT, typename... AgentParamsT>
using vsmem_helper_fallback_policy_t =
  vsmem_helper_with_fallback_impl<DefaultPolicyT,
                                  AgentT<DefaultPolicyT, AgentParamsT...>,
                                  FallbackPolicyT,
                                  AgentT<FallbackPolicyT, AgentParamsT...>>;

template <typename DefaultPolicyT, template <typename...> class AgentT, typename... AgentParamsT>
using vsmem_helper_default_fallback_policy_t =
  vsmem_helper_fallback_policy_t<DefaultPolicyT, policy_wrapper_t<DefaultPolicyT, 64, 1>, AgentT, AgentParamsT...>;

} // namespace detail

#endif // _CCCL_DOXYGEN_INVOKED

CUB_NAMESPACE_END